Multi-port Network Devices such as Ethernet, ATM or multiservice IP/MPLS Switches can support multiple broadcast domains via 802.1Q Virtual LANs (VLANs), Port-based VLANs, ATM VLANs and ELANs (Emulated LANs), or MAC address-based VLANs. When several such devices are connected together, it can be difficult to determine which physical switch ports or logical switch interfaces (such as ATM or Frame Relay Virtual Circuits or MPLS Label Switched Paths) are in the same broadcast domain, i.e., are able to receive broadcasts from other devices attached to other switch ports or interfaces. The present invention uses the learned MAC addresses, device IDs, ports or interfaces, and VLAN names or VLAN IDs (VIDs) that are learned by a Network Management System (NMS) to construct a table that accurately determines which ports or interfaces on each device are part of the same broadcast domain. This is a critical component for supporting Discovery and Provisioning of Transparent LAN Services (TLS) by a Service Provider (or large Enterprise) from any customer's LAN to other LANs belonging to the same customer via the Service Provider's network. Without such a technique, an NMS or Element Management System (EMS) could mistakenly provision switch ports or interfaces into the wrong broadcast domain/VLAN, thereby introducing network traffic from one customer's LAN into another customer's LAN. This would not only result in a security breach of the customers' networks, but could also adversely impact the customer's network routing, switching, and addressing configuration such that internal customer network services would be disrupted or disabled.